U.S. patent application number 10/701003 was filed with the patent office on 2004-05-13 for wind tunnel and collector configuration therefor.
Invention is credited to Lacey, John J. JR..
Application Number | 20040089065 10/701003 |
Document ID | / |
Family ID | 34590688 |
Filed Date | 2004-05-13 |
United States Patent
Application |
20040089065 |
Kind Code |
A1 |
Lacey, John J. JR. |
May 13, 2004 |
Wind tunnel and collector configuration therefor
Abstract
An open jet wind tunnel having a test section, a nozzle exit and
a collector in which the leading edge of the collector is
configured with at least a portion being non-uniformly spaced from
the nozzle exit.
Inventors: |
Lacey, John J. JR.;
(Minnetonka, MN) |
Correspondence
Address: |
David N. Fronek
DORSEY & WHITNEY LLP
Intellectual Property Department
50 South Sixth Street, Suite 1500
Minneapolis
MN
55402-1498
US
|
Family ID: |
34590688 |
Appl. No.: |
10/701003 |
Filed: |
November 4, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10701003 |
Nov 4, 2003 |
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10229890 |
Aug 28, 2002 |
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60315605 |
Aug 29, 2001 |
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Current U.S.
Class: |
73/147 ;
257/E29.272; 257/E29.309 |
Current CPC
Class: |
H01L 29/792 20130101;
G01M 9/04 20130101; H01L 29/78391 20140902; G01M 9/02 20130101 |
Class at
Publication: |
073/147 |
International
Class: |
G01M 009/00 |
Claims
What is claimed is:
1. An open jet wind tunnel for aerodynamic and acoustic testing
comprising: a nozzle having a nozzle opening with a nozzle opening
area, a nozzle opening perimeter and a hydraulic diameter defined
by multiplying the nozzle opening area by four and then dividing by
the nozzle opening perimeter; a collector having a leading edge
defining a collector inlet opening; and said nozzle and said
collector spaced from one another to define a test section between
said nozzle opening and said collector inlet opening, wherein said
test section has a length dimension four times or greater than the
hydraulic diameter of said nozzle opening.
2. The wind tunnel of claim 1 wherein at least a portion of said
leading edge is nonuniformly spaced from said nozzle opening.
3. The wind tunnel of claim 2 wherein said leading edge includes a
top section and a pair of side sections extending from opposite
ends of said top section.
4. The wind tunnel of claim 3 including an air flow path extending
from said nozzle opening to said collector inlet opening wherein at
least one of said side sections slopes at an angle other than 90
degrees relative to said air flow path.
5. The wind tunnel of claim 4 wherein said at least one said side
section slopes at an angle of between about 30 and 85 degrees.
6. The wind tunnel of claim 5 wherein said at least one said side
section slopes from said top section downwardly and away from said
test section.
7. The wind tunnel of claim 3 wherein said at least one side
section slopes from said top section downwardly and away from said
test section.
8. The wind tunnel of claim 2 wherein said nozzle includes an end
section with a length dimension greater than one-quarter of the
hydraulic diameter of said nozzle opening and with a substantially
uniform cross-sectional area approximating said nozzle opening area
throughout the length dimension of said end section.
9. The wind tunnel of claim 8 wherein the length dimension of said
end section is greater than one-half the hydraulic diameter of said
nozzle opening.
10. A method of constructing a wind tunnel and testing the effects
of air flow past a test vehicle in said wind tunnel comprising:
providing a wind tunnel nozzle having a nozzle opening with a
nozzle opening area, a nozzle opening perimeter and a hydraulic
diameter defined by multiplying the nozzle opening area by four and
then dividing by the nozzle opening perimeter; providing a test
vehicle with a front end, a rear end and a longitudinal axis
extending from said front end to said rear end, said test vehicle
having a maximum cross-sectional area in a plane perpendicular to
said longitudinal axis, said maximum cross-sectional area being
greater than 10% of said nozzle opening area; providing a wind
tunnel collector having a base and leading edge defining a
collector inlet opening, a portion of said leading edge being
non-uniformly spaced from a plane perpendicular to said base;
positioning said wind tunnel nozzle and said wind tunnel collector
in spaced relationship to one another so that said nozzle opening
and said collector inlet opening face one another and the distance
between said nozzle opening and said collector inlet opening
defining a wind tunnel test section which is at least four times
the hydraulic diameter of said nozzle opening; positioning said
test vehicle in said test section between said nozzle opening and
said collector inlet opening; and providing an air flow through
said nozzle opening, past said test vehicle and into said collector
inlet opening.
11. The wind tunnel of claim 10 wherein said maximum
cross-sectional area is greater than 20% of said nozzle opening
area.
12. The wind tunnel of claim 10 wherein said maximum
cross-sectional area is greater than 40% of said nozzle opening
area.
13. The wind tunnel of claim 10 wherein said test section is at
least five times the hydraulic diameter of said nozzle opening.
14. The method of claim 10 wherein said step of providing a wind
tunnel nozzle includes providing a wind tunnel nozzle having a
nozzle end section with a length dimension being greater than
one-quarter of the hydraulic diameter of said nozzle opening and
with a substantially uniform cross-sectional area approximating
said nozzle opening area throughout said length dimension.
15. The method of claim 14 wherein said length dimension is greater
than one-half the hydraulic diameter of said nozzle opening.
16. The method of claim 15 wherein said length dimension is about
three-fourths of the hydraulic diameter of said nozzle opening, or
greater.
17. An open jet wind tunnel comprising: a test section having an
upstream end and a downstream end; a nozzle having a nozzle opening
positioned at the upstream end of said test section, said nozzle
opening including a nozzle opening area, a nozzle opening perimeter
and a hydraulic diameter defined by multiplying the nozzle opening
area by four and then dividing by the nozzle perimeter, and said
nozzle further including an end section with a length dimension
greater than one-quarter of the hydraulic diameter of said nozzle
opening and with a substantially uniform cross-sectional area
approximating said nozzle opening area throughout the length
dimension of said end section; and a collector spaced from said
nozzle and having a leading edge non-uniformly spaced from said
nozzle opening.
18. The wind tunnel of claim 17 wherein the length dimension of
said end section is greater than one-half the hydraulic diameter of
said nozzle opening
19. The wind tunnel of claim 18 wherein said leading edge includes
a top section and a pair of side sections extending from opposite
ends of said top section.
20. The wind tunnel of claim 19 including an air flow path
extending from said nozzle opening to said collector inlet opening
and wherein at least one of said side sections slopes at an about
30 to 85 degrees relative to said air flow path.
21. A method of aerodynamic and acoustic testing of an automotive
vehicle comprising: providing an open jet wind tunnel having a
nozzle, a collector and a test section between said nozzle and said
collector, said nozzle having a nozzle exit area and said collector
having a leading edge with a portion being non-uniformly spaced
from said nozzle opening; providing a test automotive vehicle
having an exterior configuration and positioning said vehicle in
said test section; providing an air flow of about 5 to 200 miles
per hour from said nozzle, through said test section past said
vehicle; collecting air flow and acoustic data resulting from said
air flow past said vehicle; and evaluating said air flow and
acoustic data.
Description
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 10/229,890 filed Aug. 28, 2002 (currently
pending) which claims the benefit of Provisional Application Serial
No. 60/315,605 filed Aug. 29, 2001.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Art
[0003] The present invention relates generally to a wind tunnel and
to a collector design therefor, and more particularly to an open
jet wind tunnel with a collector design to reduce resonance in
aerodynamic and acoustic testing applications. The invention also
relates to a method of providing a wind tunnel and exposing test
objects to the wind tunnel air flow for aerodynamic and acoustic
testing.
[0004] 2. Description of the Prior Art
[0005] An existing and well-recognized problem with many open jet
wind tunnels is the pulsing or resonance which occurs at various
frequencies under certain operating conditions. Open jet wind
tunnels are used extensively in the automotive industry and various
other industries for the purpose of determining aerodynamic forces
on a test vehicle or other object and for the purpose of
determining the effect of air flow on the aerodynamic and acoustic
performance of a particular vehicle design. A typical configuration
of an open jet wind tunnel includes a test section often comprising
a large room or other closed configuration, a nozzle at the
upstream end of the test section and a collector at the downstream
end of the test section. Generated air flow flows along a flow path
from the nozzle, across the test section and into the collector.
During a test, the vehicle or other object to be tested is
positioned in the test section within the air flow.
[0006] An observed problem with many open jet wind tunnels which
often restricts their use at certain air speeds includes a pulsing
phenomenon or resonance which occurs at such air speeds. This
pulsing or resonance, in some cases, may simply make the air flow
and the floor pressures unsteady or variable so as to adversely
affect the air flow past the test object. This can result in
inaccurate and thus unreliable data. In other cases, the pulsing or
resonance may be strong enough to damage the building structure.
Various authorities have recognized this problem in open jet wind
tunnels and have speculated that such pulsing phenomenon or
resonance is directly related to test section air speeds and wind
tunnel dimensions and that the mechanism that excites such
resonance involves the interaction of vortices of air flow from the
nozzle to the collector. It has also been speculated that
decreasing the length of the test section at a given air speed will
have the tendency to reduce resonances at that air speed. However,
this is a limitation on the capability of the system and is often
not an option because of the test section length needed for a
particular application. Accordingly, to the extent that this
problem has been addressed, it has been primarily addressed by
adjusting air speeds and/or wind tunnel and test section dimensions
in an attempt to avoid the undesirable resonance problems. The
result, however, is that this merely changes the frequency or air
speed conditions at which the resonance or the pulsing phenomenon
occurs or places other significant limitations upon the system.
[0007] Even when resonance problems have been addressed as provided
above, utilization of a wind tunnel for providing air flow tests on
a test object such as a vehicle involves providing a wind tunnel
with a certain size, including nozzle size and test section length
relative to the test vehicle, so that it accurately and reliably
simulates road conditions for the particular vehicle performance
parameter being tested. This is particularly critical when the wind
tunnel is being used in the aerodynamic and acoustic testing of
vehicles as discussed below.
[0008] Automotive designers and manufacturers utilize open jet wind
tunnels to test vehicle performance in various performance areas.
One such area involves evaluating or testing the effect of air flow
on its ability to cool the vehicle engine. This is sometimes
referred to as "climatic" testing or testing conducted in
"climatic" wind tunnels. In climatic testing, the designer is
concerned primarily with the cooling effect of air flow at the "A"
pillar (the front) of the vehicle where the air enters the engine
area or other air intake and is less concerned, if at all, with any
aerodynamic or acoustic effect the air flow may have on the
vehicle. Thus, a wide range of wind tunnel sizes (in terms of
nozzle size relative to vehicle size and test section length
relative to nozzle size) can be used for climatic wind tunnel
testing on vehicles.
[0009] A second performance area involves evaluating or testing the
aerodynamic and acoustic effect of the air flow as it flows past
the vehicle. In aerodynamic and acoustic testing, the design of
windshield wipers, the design of radio antennas, the overall
exterior configuration of the vehicle from the front to the rear,
the effect of open vs. closed windows, etc. are important. As a
result, wind tunnels designed for use in, or used in, the
aerodynamic and acoustic testing of vehicles requires careful
design to ensure accurate simulation of road conditions at the
applicable speeds and thus reliable design data. Thus, in contrast
to wind tunnels used for climatic testing purposes, wind tunnels
used for aerodynamic and acoustic testing purposes have heretofore
required a relatively narrow range of wind tunnel sizes (in terms
of nozzle size relative to vehicle size and test section length
relative to nozzle size).
[0010] In general, for wind tunnels utilized in aerodynamic and
acoustic testing purposes, the size of the nozzle opening and the
distance between the nozzle and the collector (the test section
length), and thus the overall size of the wind tunnel, is dictated
by the size of the test object or vehicle. Specifically, to achieve
accurate and reliable results and to avoid resonance problems for
aerodynamic and acoustic testing, the consensus is that the
"blockage" of the test object (the cross-sectional area of the test
object in the air flow) should not exceed 10% of the nozzle opening
and that the overall length of the test section should not exceed
about three to three and one-half times the hydraulic diameter of
the nozzle opening. Thus, a test object with a "blockage" of
twenty-five square feet (25 sq. ft..sup.2) requires a nozzle
opening of at least about 250 ft..sup.2 (and thus at least a
hydraulic diameter of about 16 ft.) and an overall test section
length no more than 48 to 56 feet for reliable aerodynamic and
acoustic testing. In many cases, this significantly limits the
length of the test object or vehicle that can be tested in that
particular wind tunnel.
[0011] Accordingly, there is a need in the art for a wind tunnel
construction, and in particular an open jet wind tunnels for
aerodynamic and acoustic testing of vehicles or the like, which not
only minimizes, but preferably eliminates, resonance problems for
desired air speed and the wind tunnel dimensions, and which
provides improved space efficiency and thus reduced capital and
operating expenses.
SUMMARY OF THE INVENTION
[0012] In contrast to the prior art, the present invention is
directed to an open jet wind tunnel design, and more particularly
to a collector design and a combination collector/nozzle design for
use in such wind tunnel, which minimizes, if not eliminates,
resonance problems such as those described above for particular
applications, such as the aerodynamic and acoustic testing of
vehicles, while at the same time facilitating a significant
reduction in the size of the wind tunnel for a particular
application.
[0013] Specifically, the present invention focuses on the belief
that the resonance is created at various frequencies as a result of
eddies or other air flow between the exit edge of the nozzle exit
and the leading edge of the collector. In conventional collector
design, these edges are all uniformly spaced from one another.
Thus, the speculation is that they combine their energies to excite
and result in the undesirable resonance. In accordance with the
present invention, the collector is designed and configured so that
the spacing between the exit nozzle and the leading edge of the
collector varies (or is non-uniform) from point to point along the
collector edge. Thus, there is insufficient energy at any one
frequency to excite an undesirable resonance.
[0014] In accordance with a preferred embodiment of the present
invention, one or more sections of the leading edge of the
collector are sloped relative to the exit nozzle and relative to a
vertical plane orthogonal to the flow path of the air. Thus, air
flowing from the exit nozzle toward the collector strikes the
leading edge of the collector at different times because of the
non-uniform spacing and therefore limits or suppresses the
generation of undesirable resonance. In a most preferred embodiment
of the invention, the leading edge of the collector includes a top
edge section which is uniformly spaced from the exit nozzle, and a
pair of sloping side edge sections which slope downwardly and away
from the top section and thus results in a leading edge in which
the distance from such edge to the exit nozzle or the above
mentioned plane is non-uniform.
[0015] The invention also includes combining the collector design
with a nozzle configuration which provides a substantially ordered
air flow as it exits the nozzle opening. In the preferred
embodiment, this ordered air flow is provided by a nozzle outlet
end or extender which is of a substantially uniform cross-sectional
area for a distance measured in the direction of air flow of at
least about one-half of the hydraulic diameter of the nozzle
opening.
[0016] With this combination collector and nozzle design, the
overall wind tunnel size can be significantly reduced for a given
test object or vehicle size, or the size of the test object that
can be reliably tested can be significantly increased for a given
size wind tunnel.
[0017] Accordingly, it is an object of the present invention to
provide an improved open jet wind tunnel.
[0018] Another object of the present invention is to provide an
open jet wind tunnel with a configuration which, minimizes, if not
eliminates, undesirable resonance.
[0019] A further object of the present invention is to provide an
open jet wind tunnel with an improved collector design which
minimizes, if not eliminates, undesirable resonance.
[0020] A still further object of the present invention is to
provide a collector design for an open jet wind tunnel in which
points along the leading edge of the collector are non-uniformly
spaced from the nozzle.
[0021] Another object of the present invention is to provide a wind
tunnel with a combination collector and nozzle design which
facilitates a significant reduction in wind tunnel size for
aerodynamic and acoustic testing purposes.
[0022] Another object of the present invention is to provide an
improved method of testing a test object in a wind tunnel for
aerodynamic and acoustic testing purposes.
[0023] These and other objects of the present invention will become
apparent with reference to the drawings, the description of the
preferred embodiment and method and the appended claims.
DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a plan view of the wind tunnel in accordance with
the present invention.
[0025] FIG. 2 is an isometric view of the test section components
of the wind tunnel showing the nozzle, the test section and the
collector.
[0026] FIG. 3 is an elevational side view of the test section
components of the wind tunnel.
[0027] FIG. 4 is a plan view of the test section components of the
wind tunnel.
[0028] FIG. 5 is an elevational end view of the nozzle, as viewed
in the upstream direction, in accordance with the present
invention.
[0029] FIG. 6 is an elevational end view of the collector, as
viewed in the downstream direction, in accordance with the present
invention.
[0030] FIG. 7 is a view, partially in section, as viewed along the
section line 7-7 of FIG. 6.
[0031] FIG. 8 is a plan view of an alternate embodiment of a
collector design.
[0032] FIG. 9 is an elevational side view of the wind tunnel,
similar to FIG. 3, but showing nozzle extenders.
[0033] FIG. 10 is an elevational end view of a further embodiment
of a collector design in which the bottom lead edge has been
eliminated.
[0034] FIG. 11 is a further elevational side view of test section
components of a wind tunnel.
[0035] FIGS. 12A, 12B, 12C and 12D are schematic illustrations of
various leading edge configurations.
DESCRIPTION OF THE PREFERRED EMBODIMENT AND METHOD
[0036] The present invention relates generally to an open jet wind
tunnel design and more particularly to a wind tunnel design having
a collector design and a combination collector/nozzle design which
substantially reduces or eliminates resonance problems and which
also facilitates significant reduction in overall wind tunnel size
for a given test object size or facilitates testing of
significantly larger test objects for a given wind tunnel size.
Although the open jet wind tunnel of the present invention has a
variety of applications and can be used in virtually any
application to test the reaction of a test object to an air flow,
it has particular application to the automotive industry for
aerodynamic and acoustic testing of automobile and other vehicle
configurations in air flows ranging from approximately 5 miles per
hour to as high as 200 miles per hour or more. In such
applications, the test object is an automobile or other vehicle
with a cross-sectional area measured perpendicular to the path of
the air flow. This cross-sectional area for a test vehicle ranges
from about 15 to 120 square feet, more preferably from about 15 to
75 square feet and most preferably from about 15 to 50 square feet.
Such test vehicle also has a length dimension measured parallel to
the path of the air flow which ranges from about 10 to 60 feet and
more preferably from about 10 to 40 feet.
[0037] Throughout the application, the term "blockage" as applied
to the test object or vehicle and the term "hydraulic diameter" of
the nozzle opening will be used. As used herein, unless otherwise
specified, the term "blockage" as applied to a test object shall be
the maximum cross-sectional area of such test object as measured in
a direction perpendicular to the air flow path through the test
section. As used herein, unless otherwise specified, the term
"hydraulic diameter" as applied to the nozzle opening will be the
area of the nozzle opening multiplied by four and then divided by
the perimeter of the nozzle opening. With this definition of
hydraulic diameter, the hydraulic diameter of a circle will be its
diameter and the hydraulic diameter of a square will be the length
of one of its sides. The term "aerodynamic and acoustic" testing of
a vehicle or other test object, unless otherwise specified, shall
mean setting up, collecting and evaluating air flow and acoustic
data resulting from positioning the test vehicle or other object in
a wind tunnel at applicable air flow speeds.
[0038] Reference is first made to FIG. 1 showing a top plan view of
the wind tunnel in accordance with the present invention. The wind
tunnel 10 includes a flow generator means which is commonly in the
form of a fan 12, a heat exchanger or heat exchanger assembly 14, a
plurality of turning vanes 13 and 17, one or more flow conditioning
elements 15, a nozzle 16, a test section 18 and a collector 19.
During operation, the fan 12 is driven by a motor drive to create a
high velocity air flow stream 22 in the flow duct 20. The actual
air speed which is generated varies greatly depending on the
intended use for the wind tunnel; however, typical values range
from as low as 5 miles per hour or lower to several times the speed
of sound. Although the wind tunnel of the present invention has a
variety of applications, it has particular applicability to
providing aerodynamic and acoustic testing for the automotive
industry. When used in connection with the automotive industry, the
air speed normally ranges from about 5 to 200 miles per hour.
[0039] The preferred embodiment utilizes a fan to accelerate the
air because of its ability to move large volumes of air. However,
those skilled in the art will realize that various alternate flow
generating means can be used as well such as blowers, compressors,
diffusers, nozzles, vacuum tanks, high pressure storage chambers
and various combinations thereof.
[0040] The motor drive powers the flow generator or fan 12. Because
some of the energy supplied by the motor drive and the fan 12 is
converted into heat, a heat exchanger 14 is provided. The
temperature of the air leaving the heat exchanger 14 will vary
depending upon the intended application of the wind tunnel and the
velocity of the air flow involved; however, a typical temperature
for air exiting the heat exchanger 14 for automotive applications
is in the range of -50 to +60.degree. C. After leaving the heat
exchanger, the air flow stream 22 travels through the turning vane
13 which changes the flow direction of the flow stream 180 degrees
and into the flow conditioning elements 15. The flow conditioning
elements 15 straighten the flow stream 22 to further reduce any
turbulence. The preferred embodiment contemplates the use of a
honey comb style flow straightener. However, depending upon the
wind tunnel application, the flow conditioning elements could be
eliminated or replaced by other devices.
[0041] Upon leaving the flow conditioning elements 15, the flow
stream 22 is further accelerated through the nozzle 16 before
exiting the nozzle and entering the test section 18. During use,
the flow stream 22 passes over a test object in the test section 18
before being returned by the collector 19 to the flow duct 24,
through the turning vane 17 and back to the flow generator 12.
[0042] In the preferred embodiment the wind tunnel is a closed
circuit wind tunnel in which the wind (or air) is continuously
circulated through the system along the air flow stream. It is
understood, however, that many of the concepts and features of the
present invention may be equally applicable to wind tunnels which
are not of the closed circuit type. In actual construction and use,
the test section 18 is defined by a test section room or
containment which totally surrounds the test section 18 and is
larger than the nozzle 16 and the collector 19.
[0043] Reference is next made to FIGS. 2, 3 and 11 illustrating the
test area components of the wind tunnel. These comprise the nozzle
or tunnel assembly 16, the test section 18 and the collector 19.
With specific reference to FIG. 11, the overall length OL of the
test section 18 extends from the outlet end of the nozzle 16 to the
inlet at the base of the collector 19. This test section length OL
is comprised of a forward clearance length FC, a vehicle test
length VT, a rear clearance length RC and a pressure rise length
PR. FIGS. 3 and 11 also show a test vehicle or object 23 located in
the test section 18. As used herein, the vehicle test length VT
shall mean the maximum vehicle length that can be tested while
still obtaining accurate and reliable aerodynamic and acoustic test
data.
[0044] In general, as air flows from the nozzle opening through the
test section 18, the distance FC is required to avoid influence of
the vehicle on the nozzle flow and to ensure minimal influence of
the nozzle on the measurements on the vehicle. In general, it is
expected that the front clearance length FC for most wind tunnels
will be about three-fourths of the hydraulic diameter of the nozzle
opening. After the air flow passes the test vehicle 23 with a
length which may be less than but which may not exceed the vehicle
test length VT, a certain distance is needed in the form of the
rear clearance length RC to avoid influence of the pressure rise on
the measurements on the vehicle. Following this, the pressure
begins to increase in the area PR as the air approaches the
collector 19. In general, the combined length of the sections RC
and PR in most wind tunnels is expected to be about one to three
times the hydraulic diameter of the nozzle opening.
[0045] With reference to FIGS. 2, 3, 4 and 5, the nozzle or tunnel
assembly 16 includes a plurality of sloping walls 25 which converge
in the direction of the air flow 22 toward a nozzle exit member 26.
The nozzle exit member 26 includes a side wall which extends
generally parallel to the air flow for a short distance and
terminates at an air flow exit end 28 (FIG. 5). The air flow exit
end 28 defines the air flow exit opening 29 through which the air
flow passes before being exposed to the test object 23. In the
preferred embodiment, the exit end 28 lies in a plane generally
perpendicular or orthogonal to the movement of the air flow 22
through the nozzle assembly 16. The nozzle 16 of the preferred
embodiment includes four shaped and converging walls 25 to
accelerate the air flow and four side walls defining the nozzle
exit member 26. Thus, the cross sectional configuration of the
nozzle assembly 16 cut along a plane generally orthogonal to the
air flow is rectangular. Such cross sectional configuration, and
thus the number and configuration of the walls 25 and 26, however,
may be modified depending upon the characteristics of air flow
desired and the specific application of the wind tunnel.
[0046] If desired, nozzle extenders 40 as shown in FIG. 9 can be
utilized to vary the length of the test section 18 so as to
accommodate certain test vehicles or objects and to control
resonances at certain air flow speeds as will be discussed in
greater detail below. The nozzle extenders 40 are generally tubular
elements having a preferred cross-sectional size and configuration
substantially matching that of the nozzle outlet 28 and a length
which provides the desired air flow characteristics (and
elimination of resonances) at the desired air flow speed, test
section length and collector configuration.
[0047] In general, the preferred embodiment of the present
invention contemplates a nozzle end in the form of the nozzle exit
member 26 (FIGS. 2 and 3) or the nozzle extender 40 (FIG. 9) which
is of sufficient length relative to the size of the nozzle opening
29 (FIG. 5) to provide a substantially ordered air flow as the air
leaves the end 28 of the nozzle. By the term "ordered", it is meant
that the air flow which exits from the end 28 of the nozzle
exhibits a substantially uniform velocity profile. In other words,
the velocity of the air flowing from the end 28 of the nozzle is
substantially uniform over substantially the entirety of the nozzle
opening 29. It is recognized that this is a matter of degree;
however, a substantially uniform velocity profile will be
established if the length of the nozzle exit member 26 and/or the
nozzle extender 40 have a length which is at least one quarter of
the hydraulic diameter of the nozzle opening and more preferably at
least about one half the hydraulic diameter of the nozzle opening.
Most preferably, the length of the nozzle exit member 26 or the
nozzle extenders 40 should be about three fourths of the hydraulic
diameter of the nozzle opening or more. In the preferred
embodiment, the nozzle exit member 26 and the nozzle extender 40
have a substantially constant or uniform cross-sectional
configuration and size throughout the entirety of their length.
[0048] The test section 18 includes a base 27 which upon the test
object 23 may be mounted and is positioned between the nozzle 16
(or the nozzle extender 40 of FIG. 9) and the collector 19. The
test section includes an upstream end adjacent to the nozzle 16 and
a downstream end adjacent to the collector 19. The test object 23
such as a vehicle or the like is positioned on, or mounted to, the
base 27, in a conventional manner. During use, the air flow 22
flows from the nozzle 16 (or nozzle extender 40), across the test
section 18 and to the collector 19 in the direction of the flow
path 22. In some applications, where the test object is suspended
from above or supported on a post or the like, the base 27 may be
eliminated.
[0049] The collector 19 is the structural element of the wind
tunnel which is positioned adjacent the downstream end of the test
section 18 and functions to return the air flow to the return duct
24. The collector 19 includes a collector housing 30 having a
rearward flange or bracket 31 for connecting the collector 19 to
the return flow duct 24. In the preferred embodiment, the housing
30 forms a generally tubular configuration with walls extending
rearwardly from the leading edge of the collector 19 in a direction
generally parallel to the air flow 22 in the test section 18. The
collector 19 also includes a forwardly positioned leading edge 32
which faces upstream relative to the air flow and which thus
engages the air flow after it passes the test object. As shown best
in FIGS. 2 and 6, the leading edge of the collector includes a
plurality of sections, namely, a top section 34, a bottom section
35 and a pair of side sections 36,36. The plurality of sections 34,
35, 36 and 36 define an air flow inlet opening 38. The opening 38
receives air passing the test object 23 in the test section 18 and
returns it to the return duct 24 for recirculation. Wind tunnels
with a leading edge on a bottom section such as the section 35 are
more common in wind tunnels without a base 27.
[0050] As shown best in FIGS. 2 and 3, the leading edge 32 has a
configuration in which the top section 34 and bottom section 35 are
generally perpendicular to the direction of air flow 22. Thus,
points along the section 34 are generally uniformly spaced from the
nozzle exit end 28 and points along the section 35 are generally
uniformly spaced from the nozzle exit end 28, but at a distance
different from one another. In contrast, the side sections 36,36
each slope downwardly and rearwardly (away from the test section
18) at an angle "A" from the top section 34 in the direction of the
air flow, Thus, points along the side sections, 36,36 are not
uniformly spaced from the nozzle exit end 28.
[0051] Although applicant does not wish to be bound to any
particular theory, it is believed that the undesirable resonance
and pulsation in existing open jet wind tunnels is a result of
eddies or other air flow between the exit edge of the nozzle exit
28 and the leading edge of the collector 19. Because these edges in
conventional and existing designs are all substantially uniformly
spaced from one another, they combine their energies to excite the
undesirable resonance. By modifying the test area structure, and in
particular the configuration of the collector 19 and thus the
leading edges of the collector 19, so that the distance between the
nozzle exit and at least a portion of the leading edges of the
collector are not uniformly spaced, there is insufficient energy at
any one frequency to excite the resonance. Accordingly, the present
invention is directed to providing a wind tunnel test area
comprising the nozzle or nozzle exit 16, the test section 18 and
the collector 19, in which the space or distance between the exit
edge of the nozzle and points along the leading edge of the
collector is non-uniform, or which at least includes sections where
such space or distance is non-uniform. Thus, the present invention
provides a test area including a nozzle with an exit edge and a
collector with a leading edge in which the nozzle exit edge and/or
the collector leading edge are configured to provide non-uniform
spacing between points along the nozzle exit edge and corresponding
points along the collector leading edge. Although it is possible
for either the nozzle exit edge or the collector leading edge, or
both, to be configured to provide this non-uniform spacing, in the
preferred embodiment, the points along the nozzle exit edge lie in
a common vertical plane. In contrast, the collector leading edge is
configured so that points along at least a portion of such edge are
non-uniformly spaced from such vertical plane.
[0052] Another way of expressing the structure of the present
invention is to define the position of the leading edge 32 of the
collector 19 relative to an imaginary plane orthogonal to the flow
path 22 of the air stream in the test section 18. Such an imaginary
plane is illustrated in FIG. 3 by the reference character 33. In
the preferred collector structure, the leading edge sections 34 and
35 are generally parallel to such orthogonal plane 33 and thus
points along the leading edge sections 34 and 35 are substantially
uniformly spaced from the plane 33. However, because the leading
edge sections 36,36 are sloped relative to the plane 33, points
along the edge sections 36,36 are non-uniformly spaced from the
orthogonal plane 33. Further, although points along the leading
edge section 34 are uniformly spaced from the plane 33 and points
along the leading edge section 35 are uniformly spaced from the
plane 33, the distances between the points on the edge section 34
and the plane 33 and between the points on the edge section 35 and
the plane 33 are different from one another. Thus, in the structure
of the preferred embodiment, only a portion (no more than about 60
percent) of the leading edge of the collector 19 is uniformly
spaced from the plane 33 or the nozzle exit. More preferably, no
more than about 50 percent of the leading edge of the collector 19
should be at a uniform distance from the plane 33 or the nozzle
exit, and most preferably, no more than about 40 percent of the
leading edge of the collector 19 should be at a uniform distance
from the plane 33 or the nozzle exit.
[0053] It should be noted that an open jet wind tunnel can have
four exposed or impact leading edge sections as shown or three
exposed or impact leading edge sections as shown in FIGS. 9 and 10
in which the base 27 of the test section is substantially
continuous with the bottom entrance to the collector 19 or any of a
variety of different configurations having various numbers of
exposed or impact leading edge sections. As indicated above, a
collector configuration with four leading edge sides (including one
on the bottom) is used primarily in open jet wind tunnels without a
base 27. The configuration shown in FIGS. 9 and 10 is preferred for
wind tunnels with a supporting base 27. Regardless of the number of
leading edge sections, the above percentages are intended to apply
only to the exposed or impact leading edges.
[0054] For purposes of determining whether a leading edge section
34, 35, 36,36 of the collector 19, or points along a leading edge
section are uniformly or non-uniformly spaced from the plane 33 or
the nozzle exit, the point considered is the stagnation point or
the point at a particular location or cross-section on the leading
edge section which is closest to the plane 33 or the nozzle exit.
The collection of these points generally follows the periphery of
the collector opening 38. Thus, points along the leading edge
section 34 would each be uniformly spaced from the plane 33 at a
first distance, and points along the leading edge section 35 would
be uniformly spaced from the plane 33 at a second distance, but
points along the leading edge sections 36,36 would be non-uniformly
spaced from the plane 33.
[0055] In the structure of the preferred embodiment shown best in
FIG. 3, the angle "A" which the leading edge sections 36,36 form
with the base 27 of the test section 18 (or the flow path 22) may
be altered or adjusted to provide optimum and desired results.
Specifically, the edge sections 36,36 slope at an angle other than
90 degrees. No particular angle "A" is necessary to accomplish the
objectives of the present invention so long as a portion of the
leading edge of the collector is non uniformly spaced from the
nozzle exit or the orthogonal plane 33. Thus, for a collector with
sloping side edges as shown, the angle "A" should be less than
85.degree., more preferably less than 75.degree. and most
preferably less than 70.degree.. The range of angle "A" which the
leading edge sections 36,36 form with the flow path 22 should
preferably be from about 30.degree. to 85.degree., more preferably
from about 40.degree. to 80.degree. and most preferably from about
50.degree. to 75.degree.. Further, although the preferred
embodiment shows the side edge sections 36,36 sloping downwardly
and rearwardly (away from the test section 18), they could also
slope downwardly and forwardly.
[0056] It is also contemplated that various leading edge
configurations, other than the angled side edge configuration shown
in FIGS. 2 and 3, may be provided to accomplish the objectives of
the present invention. For example, one or more of the edge
sections 34, 35, 36,36 could be curved or provided with any other
configuration in which points along those edge sections are spaced
at varying, non-uniform distances from the nozzle exit or
orthogonal plane 33. FIG. 8 shows a possible alternate embodiment
in which the top leading edge section is formed by two portions 34A
and 34B. As shown, the edge portions 34A and 34B are sloped at an
angle relative to the flow path 22 of the air flow. This top
leading edge configuration can be combined with vertical, sloping
or curved side edges as well as a horizontal, angled or curved
bottom edge. Examples of some possible leading edge configurations
are shown schematically in FIGS. 12A, 12B, 12C and 12D, although
others are possible as well.
[0057] The leading edge sections 34, 35, 36,36 may be comprised of
any cross sectional configuration conventional in the art. In the
preferred embodiment, as shown in FIG. 7, the cross sectional
configuration of the leading edge sections 34, 35, 36,36 (which are
all the same) is a curved configuration of a constant radius.
[0058] Although providing the collector leading edges with edge
sections which are spaced at non-uniform distances from the exit
nozzle or nozzle extender function to reduce the resonances formed
in the test section, experimental results indicate that the ability
of such a collector design to reduce or eliminate such resonances
will depend not only on the particular angle "A" at which the side
edge sections 36,36 are positioned, but also will depend on the
length of the test section 18 (the distance from the nozzle exit 28
to the leading edge of the collector) as well as the existence of
nozzle extenders 40 or exit members 26 or other means to provide
substantially ordered flow exiting the nozzle. Specifically, for a
given air flow speed, resonances are eliminated by a collector with
side edges at a certain angle "A" up to a certain test section
length. As that length is increased beyond that certain length,
resonances will again begin to appear. These resonances can,
however, be eliminated by decreasing the angle "A" which the side
edges 36,36 of the collector form with the air flow direction or by
providing a more ordered air flow exiting the nozzle.
[0059] Thus, a collector design such as that shown in the drawings
will reduce resonances in a test section over a collector design in
which all leading edges are uniformly spaced from the nozzle exit,
but only up to a certain test section length. As the angle "A" is
decreased from 90.degree. (which would define a structure in which
all leading edges are uniformly spaced from the nozzle exit),
resonances will be reduced or eliminated for a given air speed up
to a certain length. If it is desired to increase the test section
length, the angle "A" of the edge sections 36,36 is decreased or
more ordered air flow is provided at the nozzle exit.
[0060] Accordingly, by varying the angle at which the side edges
36,36 are sloped relative to the air flow direction, by varying the
test section length by adjusting the position of the nozzle 16
and/or collector 19 or by utilizing nozzle extenders 40, nozzle
exit members 26 or other means to provide more ordered air flow at
the nozzle exit, the resonances for a particular application and
particular air flow speed can be effectively reduced or eliminated.
Thus, a method in accordance with the present invention includes
providing a wind tunnel with a nozzle and a collector with at least
a portion of the leading edge of the collector being non-uniformly
spaced from the nozzle and varying the test section length, varying
the angle of the leading edge sections of the collector and/or
providing a more ordered air flow at the nozzle exit to reduce or
eliminate the resonances at a given air speed to an acceptable
level.
[0061] Although the description of the preferred embodiment and
method has been quite specific, it is contemplated that various
modifications could be made without deviating from the spirit of
the present invention. Accordingly, it is intended that the scope
of the present invention be dictated by the appended claims rather
than by the description of the preferred embodiment.
* * * * *